This invention generally relates to methods and apparatus for manufacturing flexible zippers for use in reclosable pouches, bags or other packages. In particular, the invention relates to zippers having flanges or fins, by means of which the bag making film is attached to the zipper.
Reclosable bags are finding ever-growing acceptance as primary packaging, particularly as packaging for foodstuffs such as cereal, fresh vegetables, snacks and the like. Such bags provide the consumer with the ability to readily store, in a closed, if not sealed, package any unused portion of the packaged product even after the package is initially opened.
Reclosable fastener assemblies are useful for sealing thermoplastic pouches or bags. Such fastener assemblies often include a plastic zipper and a slider. Typically, the plastic zipper includes a pair of interlockable profiled members that form a closure. As the slider moves across the profiles, the profiles are opened or closed. The profiles in plastic zippers can take on various configurations, e.g. interlocking rib and groove elements having so-called male and female profiles, interlocking alternating hook-shaped closure members, etc. Reclosable bags having slider-operated zippers are generally more desirable to consumers than bags having zippers without sliders because the slider eliminates the need for the consumer to align the interlockable zipper profiles before causing those profiles to engage.
In addition, zippers can be differentiated by whether or not the zipper strips having flanges for attachment to the receptacle. When the zipper strips have flanges (also called “fins”), it is customary that the flanges are sealed at the respective ends of the zipper, adjacent the side seals in the bag.
Flattening sliderless zippers at the package ends is common. Flattening the zipper (sometimes called “presealing”) prior to merging with the bag at a position corresponding to the package edge facilitates sealing the bag edges at the zipper. This is because the zipper is pre-flattened so that it is much easier to create a leak-resistant seal around the zipper edges.
In one type of slider-actuated zipper, the slider straddles the zipper and has a separating finger at one end that is inserted between the profiles to force them apart as the slider is moved along the zipper in an opening direction. The other end of the slider is sufficiently narrow to force the profiles into engagement and close the zipper when the slider is moved along the zipper in a closing direction. Other types of slider-operated zipper assemblies avoid the use of a separating finger. For example, U.S. Pat. No. 6,047,450 discloses a zipper comprising a pair of mutually interlockable profiled structures, portions of which form a fulcrum about which the profiled structures may be pivoted out of engagement when lower edges of the bases are forced towards each other.
One of the important features of zipper assemblies operated by sliders without separating fingers is the end stop, which prevents the clipped-on slider from falling off when the slider reaches the end of the fastener. A slider end stop is provided on each end of the zipper. End stops have taken on various configurations, such as, for example, riveted end clamps such as those described in U.S. Pat. Nos. 5,067,208 and 5,161,286; transverse end stops made from molten material of the fastener strips, as described in U.S. Pat. No. 5,088,971; tubular end stops, as described in U.S. Pat. No. 5,405,478; a window structure combined with sealed zipper ends, as described in U.S. Pat. No. 5,442,837; plastic end clips fused to the zipper, as described in U.S. Pat. No. 5,448,807; posts with enlarged heads that pass through the ends of the zipper profiles, as described in U.S. Pat. No. 5,924,173; plastic ribbon, monofilament or clip-shaped segments that conform to the outer shape of and are fused to the zipper profile, as described in U.S. Pat. No. 5,833,791
A slider end stop must be designed to withstand the force applied by a consumer during normal use. More specifically, as the consumer pulls the slider to either end of the zipper, the end stop should not bend, fold, collapse or otherwise lose its ability to stop the slider when the slider is pressed against the end stop with the pulling force being exerted by the consumer. Preferably a slider end stop has relatively high slider pull-off resistance.
In a known method of manufacture, both an ultrasonic or other shaping device and separate device for sealing the zipper flanges, e.g., by means of ultrasonics, hot bar sealer or other device, are used. This known method increases the cost and complexity of manufacture and increases the size of the overall equipment due to the presence of the additional equipment and the additional separation between devices required for packaging registration.
There is a need for improvements in the manufacture of reclosable bags having flanged zippers (with or without sliders). In particular, there is a need for reducing the cost of the equipment used to manufacture flanged zippers of the type wherein the ends of the zipper profiles need to be shaped (by deforming the plastic zipper material) and the ends of the zipper flanges need to be sealed (by fusing the plastic zipper material).